1. Field of the Invention
This invention relates generally to fluid cooling devices, and more particularly to fluid cooling devices including pluralities of superimposed cold plates for use in removing heat generated in systems, e.g., electronic systems and electronic components, and methods of manufacturing such fluid cooling devices.
2. Background
Fluid cooling devices including one or more high heat flux cold plates have been used for removing or transferring heat generated in, e.g., electronic components and/or systems during operation. Traditionally, such fluid cooling devices have been designed for providing turbulent flows of fluid near a single cold plate and/or between a plurality of parallel cold plates. This is because turbulent fluid flows generally have thinner boundary layers and more fluid mixing than laminar flows and, consequently, higher heat transfer coefficients for fully developed flow.
However, cold plates for use with turbulent fluid flows have drawbacks. For example, as the turbulence and Reynolds number, Re, of a cooling fluid increase, more pressure is generally required to pass a given volume of the fluid through the cooling device. As a result, fluid pressure drop in the direction of fluid flow increases with the square of the volumetric flow rate. In contrast, for laminar fluid flows, the fluid pressure drop in the direction of fluid flow is linearly proportional to the volumetric flow rate.
An example of a fluid cooling device including a plurality of superposed plates is disclosed in GB Patent 604, 464 (xe2x80x9cthe ""464 patentxe2x80x9d) to Girodin. In accordance with that disclosure, a heat exchange device includes the plurality of superposed plates, each plate having parallel rows of perforations between which there are parallel imperforate strips. The plates are closely applied together so that each imperforate strip of each plate is in contact with an imperforate strip of the immediately adjacent plates. Further, the rows of perforations of a plate are staggered in relation to the rows of perforations of the immediately adjacent plates. In order to provide flow paths for the exchanging fluids, the paths are parallel to the imperforate strips, which form partitions between the exchanging fluids.
Another example of a fluid cooling device including a plurality of plates is disclosed in Russian Patent SU 1,161,810 (xe2x80x9cthe ""810 patentxe2x80x9d). In accordance with that disclosure, a heat exchanger packet includes perforated plates whose perforations are displaced in adjacent plates and are joined into groups limited by frames forming channels for working media. Heat transfer is intensified and the heat exchanger is made more compact because the perforations in each channel have equivalent diameter equal to the width of the channel and are placed with a step whose length is 1.25 to 2 times the channel width. Further, the distance between the perforation centers in adjacent plates is 0.25 to 0.5 times their distance in the channel; and the plate sections between adjacent perforations in each group are bent by an angle of 1 to 6 degrees to the plate plane.
However, the conventional fluid cooling devices described in the ""464 and ""810 patents also have drawbacks. For example, typically, they cannot provide the high level of thermal performance required in today""s highly integrated and/or power dense electronic components and systems at an acceptable pressure drop and cost. This is because neither the ""464 nor the ""810 patent is concerned with how the fluid cooling device disclosed therein might be optimized for providing the highest level of thermal performance for a given type of cooling fluid flow.
For example, the disclosure given in the ""464 patent of various embodiments of fluid cooling devices has in view heat exchangers with either streamline (i.e., laminar) or turbulent fluid flow. Further, the ""810 patent teaches that heat transfer is intensified using the fluid cooling device disclosed therein through multiple movement direction variation, which is understood to refer to turbulent fluid flow. But, neither the ""464 nor the ""810 patent shows how the fluid cooling device disclosed therein might be optimized for providing the highest level of thermal performance in either the laminar or turbulent flow regime, subject to pressure drop and cost constraints. Although turbulent fluid flows normally enhance the efficiency of the heat transfer, e.g., from the cold plates to the cooling fluid, particularly in the case of fully developed flows, and although the fluid cooling devices of the ""464 and ""810 patents may be used with such turbulent fluid flows, neither the ""464 nor the ""810 patent discloses how to deal with the pressure drop and the reduced heat transfer efficiency resulting therefrom as the turbulence of the cooling fluid increases.
U.S. Pat. No. 4,807,342 describes a heat exchanger for indirect exchange between two fluid media and a method for making the same that maximizes heat exchange between the two fluid media by providing a multitude of individual, tortuous flow channels though a thin walled device. U.S. Pat. No. 5,021,924 describes a semiconductor cooling device comprising a sealed structure in which the backs of integrated circuit chips are individually cooled with forced convection using a cooling liquid wherein greater heat transfer is obtained by increasing the velocity gradient and controlling the angle of impingement of the coolant when it strikes the back of the IC chips. Neither of these inventions addresses pressure drop and/or the advantages of laminar flow over turbulent flow in heat exchange.
Because of increased power dissipation needs of modern electronic packages, there is a continued need for new, more efficient and cost effective methods and cooling devices.
The present inventors have recognized that, although heat transfer in fluid cooling devices including a plurality of cold plates generally is more efficient with turbulent fluid flow, improved thermal performance can be achieved by configuring the fluid cooling devices to support laminar fluid flow, particularly, when the flow boundary layer is developing. Significantly, it has been discovered that fluid cooling devices configured for use with laminar fluid flows can provide improved thermal performance without the high pressure drop that often results in conventional fluid cooling devices that utilize turbulent flow regimes.
In accord with the present invention, contrary to conventional practice, a fluid cooling device is configured for use preferably with laminar, particularly developing laminar fluid flows, thereby providing both high thermal performance and low pressure drop. The present invention also provides a simple and lower cost method of manufacturing such fluid cooling devices.
Thus, the present invention provides a fluid cooling device comprising a plurality of superimposed cold plates having an alternating, or staggered, pattern for forming alternate parallel paths of fluid flow. Preferably, the fluid cooling device of the present invention is structured and arranged to utilize laminar, developing fluid flows, thereby delivering high thermal performance with low pressure drop. The present invention also provides a simplified, flexible process for manufacturing the fluid cooling device that is not only relatively inexpensive to implement, but can also be used to design and configure fluid cooling devices suitable for use with a wide range of systems and components having a wide range of performance and cost requirements.
According to one embodiment of the present invention, a fluid cooling device includes a plurality of cold plate members or stack of cold plate members, each cold plate member or stack of cold plate members including at least one plate portion and at least one perforate portion, wherein the plurality of cold plate members or stack of cold plate members is disposed causing the plate portion of each cold plate member to be in registration with respective perforate portions of adjacent cold plate members in the stack, and wherein the length of the plate portion of each cold plate member is less than the length of the perforate portion in a direction parallel to a fluid flow, the length of the plate portion of each cold plate member being set so that boundary layers growing near opposing surfaces of adjacent plate portions in the stack do not merge during flow along the entire length of the opposing surfaces, thereby providing laminar flow over the entire length of those surfaces.
Preferably, before the boundary layers have a chance to merge, i.e., fully develop, the structure of the fluid cooling device breaks, or interrupts, the flow and re-starts the boundary layer growth process. The dimensions of the structure are designed by well known heat conduction and fluid flow relationships according to the properties of the cooling fluid used. The fluid cooling device then operates continuously in, preferably, the laminar, developing or entry region flow regime. Advantageously, the performance in the laminar, developing, or entrance region can far exceed that of fully developed laminar flow, and in many cases turbulent flow as well.
The above-described embodiment of the fluid cooling device can significantly improve heat transfer via convection from the fluid cooling device to a coolant flowing over and through the fluid cooling device, while reducing pressure drop in the direction of fluid flow, in comparison with thermally comparable prior art turbulent flow cooling device designs.
According to another embodiment of the present invention, a method of manufacturing a fluid cooling device includes the steps of (i) forming a plurality of identical cold plate members; (ii) positioning the plurality of cold plate members relative to each other by alternating the cold plate members (or stack of cold plate members) so that each cold plate member is the reverse, xe2x80x9cmirror imagexe2x80x9d of any adjacent cold plate members (or stack of cold plate members) and, moreover, so that respective plate portions of each cold plate member are in registration with perforate portions formed in adjacent cold plate members and the dimensions of fluid paths are such that the fluid is substantially continuously, preferably, in laminar flow; and (iii) joining each cold plate member with its adjacent cold plate members, thereby forming the fluid cooling device.
The above-described embodiment of the method of manufacturing a fluid cooling device is relatively simple and inexpensive to implement, thereby allowing the manufacture of relatively low-cost fluid cooling devices for accommodating a wide range of designs and performance requirements. Still further aspects and advantages of the present invention will become apparent from a consideration of the ensuing description and drawings. Through design this technology allows for easy tailoring of cold plates for specific fluids and flow rates.